In automatic industrial on-line analysis by liquid phase chromatography, a sample is taken from the liquid medium to be analyzed, with the aid of a probe, and this sample is conveyed by means of at least one pump through a circulation circuit or sampling line comprising tubes, filters, valves, connections, etc . . . Such a circuit is intended to take the sample towards a chromatograph in liquid phase located geographically at a certain distance from the point of sampling.
This technique is generally satisfactory when the liquid medium to be analyzed is homogeneous. On the other hand, in the case of taking a sample in a heterogeneous medium comprising, for example, a solid or polymeric phase dispersed in a liquid, clogging, fouling, blocking and even seizure of mobile elements of the sampling line very often occur. Such incidents result in a loss of reliability and credibility of the analysis effected and, furthermore, considerably increase maintenance of the analysis device or installation.
In an attempt to minimize this constraint, it is usually sought to reduce the length of the sampling line by recommending an installation of the type shown in FIG. 1, which represents the known state of the art. In this Figure, an on-line analysis installation comprises means 1 for taking and filtering a sample from a vessel 2 for storage or reaction of the liquid product 3 to be analyzed. Means 1 are connected by a sampling line 4 to an analysis unit 5 which is generally disposed on the site of the vessel 2, so as to reduce as much as possible the length of this line 4. The analysis unit 5 comprises means for injecting the sample and the liquid vector fluid by pump 6, one or more separation columns and detection means. The unit 5 is electrically connected to a remote monitoring unit 7 which assesses the results of analysis and controls the modification of the operational parameters of the industrial process as a function of the analytic characteristics noted.
For such an installation to operate satisfactorily, it is know that the analysis must be carried out under constant conditions of temperature and of flowrate of the vector fluid. Now, by placing the analysis unit 5 as close as possible to the site of the vessel 2, it is readily appreciated that the variations in temperature of the industrial premises will have a detrimental influence on the development of the analysis sequences. This is why it is usual to construct the unit 5 in the form of a temperature-regulated assembly.
In reality, such means lead to an installation which is particularly delicate to operate, is expensive and of which the maintenance must necessarily be carried out by highly qualified personnel. In addition to this negative aspect, it should be noted that the means recommended do not make it possible to eliminate completely the sampling line 4 of which the drawbacks set forth hereinabove remain.
It should also be pointed out that the existence of a relatively long sampling line 4 most often involves a continuous taking and treatment of samples, this on the one hand representing a considerable consumption of the liquid medium to be analyzed and, on the other hand, poses a problem of evacuation of this continuous sampling when it is question of a product of polluting or non-recycyable nature.